Application of self-organizing map (SOM)-based approach to explore the relationship between land use and water quality in Deqing County, Taihu Lake Basin

Abstract

Characterizing the spatial patterns of surface water quality is of great significance for water resources management and protection. A great number of studies have addressed the fact that water quality is often subjected to surrounding land use patterns, but the relationship between them remains obscure. In this study, we develop a self-organizing map (SOM)-based approach to explore the relationship between land use and water quality in Deqing County, Zhejiang Province, which locates in the hinterland of the Yangtze River Delta in the Taihu Lake Basin. Water samples were collected from 163 streams, ponds or lakes and then clustered into six groups based on five water quality variables: pH, ammonium-N, total phosphate, dissolved oxygen and permanganate index using the SOM approach. The proportion of eight land use categories, which are forest, cropland, shrubland, grassland, water, wetland, impervious land and bare land were associated with water quality to explain its spatial variation. The altitude decreases from west to east and the eastern part of Deqing County is characterized by floodplain and streams network, which makes watershed delineating real hard work. Therefore polder and multiple buffer scales were considered to carry out the spatial discretization process. For land use parameters, sub-watershed scale was surpassing buffer scale in the elevated area, but only buffer scale can be applied in the whole area. Polders totally failed to reveal the relationship between land use and water quality. Our results demonstrate whether point source (PS) or non-point source (NPS) pollution exerts greater influence on water quality in different clusters. The methods and the results demonstrated in this research can help local government improve water resources and land use management strategies practically.